1. Field of the Invention
A conventional mass spectrometer is constructed as generating an ion of the analyzing sample outside in the air and injecting it into the inside of the vacuum chamber by using devices such as Electrospray Ionization (ESI) or Matrix Assisted Laser Desorption Ionization (MALDI). Guiding the injected ions to the detection unit located in the ultra-high vacuum stage in which an actual analysis is performed, ions could be detected and analyzed.
Specifically, the devices such as Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FT-ICR MS) is comprised of a long ion guide located between the exterior ion injection device and a high magnetic field region in which a detection is performed, and the transmission efficiency of such devices are highly affective on the detection sensitivity of the entire device.
There are two types of generally used ion guides including an electrostatic lens form and an RF multi-pole form.
The present invention relates to a method of stabilizing the ultra-high vacuum stage by locating an electrostatic ion guide, an RF ion guide and a gate valve between those two ion guides, as well as improving the transmission efficiency of the RF ion guide by using the focusing electrostatic ion guide.
2. Description of the Related Art
Since there are relatively large number of electrodes to be controlled, not allowing the ions to deviate from the original path, by means of focusing the ions which are under transmission, the form of an electrostatic ion guide has many optimization parameters, and it also has a defect that the design should be modified according to the constitutional change of the peripheral devices such as the replacement of a superconducting magnet. Particularly, in the high magnetic field over 15 Tesla, if the ions are not focused, the ions leap out again from an increasing incident angle due to the magnetic mirror effect of the ions in a high magnetic field gradient.
In order to improve the ion transmission in such a high magnetic field, it should be optimized by requiring more time for adjusting the voltage of an ion guide.
The form of an RF ion guide as the form of a linear ion trap, could be simply optimized since a few parameters need to be controlled, in which ions are transmitted while confining their movements in a vertical direction to the ion transmission direction by applying an RF voltage, and only permitting the parallel movement along the multi-pole RF ion guide central axis, and also there is an advantage that additional design is not required and only the multi-pole's length need to be adjusted in accordance with the constitutional change of the peripheral devices such as the replacement of a superconducting magnet.
However, partial ions loss could be incurred in a FT-ICR MS which should pass through the region with the variation of the magnetic field. There have been continuous requirements that such problems related to the ion guide needs to be improved. Also, in a FT-ICR MS device, it is general that a gate valve is disposed in the middle of the ion guide system to separate the ultra high vacuum region from relatively low vacuum region. The equipment of this gate valve necessarily separates the ion guide into two isolated ion guides physically, so that it affects the ion path passing through the gate valve to reduce the ion transmission efficiency.
The first method among the various methods which are conventionally being attempted to minimize such a loss is that, making all of the ion guides with an electrostatic lens system to pass through the gate valve. In this case, ion transmission is totally dependent upon an electrostatic ion guide system from the ionization source to the detection unit.
The second method uses an RF multi-pole device as an ion guide, and solved the reduction problem of the ion transmission efficiency passing through the gate valve by minimizing the thickness of the gate valve. Similarly, the RF ion guide is used, and when the gate valve is to be closed, the center part of the RF ion guide is separately moved away from the gate valve, and when the gate valve is to be opened, it is moved again almost to connect the two RF ion guides being slightly separated. However, there have been many difficulties in using those methods, such that the devices are complicated and it is hard to fabricate.